1. Field of the Invention
The present invention relates to a golf club head having a structure being capable of increasing the degree of freedom of design and the degree of freedom of selecting materials.
2. Description of the Related Art Including Information Disclosed under 37 CFR 1.97-1.99
Conventionally, wood-shaped metallic golf club heads are formed by welding metallic parts together. Such club heads are disclosed in the following prior arts.
In U.S. Pat. No. 5,024,437 (Patent date: 18 Jun. 1991, Filing date: 13 Mar. 1990), a golf club head having a two-piece structure is disclosed, wherein the two pieces are a face plate and a main body. The face plate is fabricated of forged carbon steel, forged stainless steel, forged berylium copper or forged titanium. The main body is formed by investment casting of stainless steel, beryllium copper, titanium, aluminum or the like.
In Japanese patent No. 3135396 (Issue date: 1 Dec. 2000, Laid-open date: 21 Jun. 1994, Filing date: 4 Dec. 1992), a golf club head having a two-piece structure is disclosed. In this case, the head is hollow, and the two pieces are a face plate and a main body. The main body is formed by casting of a titanium alloy. The face plate is fabricated of rolled or forged titanium alloy which is different from the titanium alloy of the main body.
In the laid-open Japanese patent application JP-A-3-51065 (Laid-open date: 5 Mar. 1991, Filing date: 19 Jul. 1989), a golf club head having a two-piece structure is disclosed. In this case, the head is also hollow, and the two pieces are a bottom-opened main body and a sole plate closing the bottom. The main body is formed by casting of titanium or a titanium alloy. The sole plate is fabricated of pressed titanium or a pressed titanium alloy.
In general, castings have a tendency to decrease the strength sharply when the thickness is decreased beyond a certain value due to crystal structure and material imperfection such as air holes. Thus, it is necessary to design the thickness somewhat greater.
In the hollow club heads as in the later two prior arts, therefore, it is difficult to decrease the thickness of the crown for the purpose of lowering the center of gravity, and decrease the thickness of the face for the purpose of improving the restitution coefficient. Further, it is difficult to optimize the position of the center of gravity, weight distribution, moment of inertia and the like of the head. Thus, the freedom of designing the head is considerably limited.